Contact bank for a switching device



June 6, 1967 D. LA ROY 3,324,269

CONTACT BANK FOR A swmcnme DEVICE Filed Nov. 1, 1965 Fig. 1

Fig.2

INVENTOR DICK LA ROY AGENT v United States Patent 3,324,269 CONTACT BANKFOR A SWITCHING DEVICE Dick la Roy, Enschede, Netherlands, assignor toN. V.

Hollandse Signaalapparaten, Hengelo, Overijsel, Netherlands, a firm ofthe Netherlands Filed Nov. 1, 1965, Ser. No. 505,845 Claims priority,application Netherlands, Nov. 2, 1964, 6,412,706 5 Claims. (Cl. 200-166)The invention relates to a contact bank for a switching device and to amethod for making the same.

Generally a contact bank for a switching device is built by mountingeach of the contact elements separately onto the switching device. Ifthese contact elements are not adjacent, as will generally be the casein digitalising switches, the contact elements are either countersunkinto a layer of isolating material, or parts of isolating material aremounted between non-adjacent contact elements, care being taken that thesurfaces of the contact elements and that of the isolating material arein the same plane. Contact banks of this type have variousdisadvantages. Their construction requires much work and is, therefore,relatively expensive. It is very difiicult to build small switches inthis way, and yet in many cases, for instance in building digitalisingswitches, small dimensions are highly desirable. Moreover, the isolatingmaterial wears more rapidly than the material of the contact elements,which causes the switching devices to become obsolete very soon.Especially in contact devices in which rapidly moving contactarrangements cooperate with the contact banks the unevenness of thecontact banks caused by wear will make the contact devices vibrate, sothat no reliable contact can be established. Moreover the pulverisedmaterial which is produced by the wear of the isolating parts of thecontact bank will smudge the contact elements and this is prejudicial tothe reliability of the contact between the contact arrangements and thecontact bank. Moreover it is very difficult to arrange the contactelements in small switching devices with suflicient accuracy such thatthe switching manipulations will take place in well-defined positions ofthe contact arrangements.

The invention substantially obviates the above drawbacks. According tothe invention the contact bank comprises a number of metal contactelements which, in the form of a precipitation of metal, are fixedlyconnected to an aluminium surface carrying these contact elements, thepart of the aluminium surface situated beyond the contact elements beingcovered by an anodised layer, at any rate in so far as the area overwhich any contact arrangement cooperating with the contact bank movesdurin g the relative motion of contact arrangement and contact bank isconcerned.

The anodised layer is not only an excellent isolator but is, moreover,very resistant to wear. Consequently it is possible for the surface ofthe anodised layer and the surface of the contact elements to remain inthe same plane without any unevenness after these surfaces have beenmade even and smooth by grinding, polishing or lapping, so that during arelatively long life of the switching device all unevenness in theregion of the separations between the anodised surface and the contactsurface will be avoided. For this reason the contact bank according tothe invention constitutes an important improvement in rapidly movingswitching devices.

According to the invention the contact bank described above can beproduced by the following method. Firstly the aluminium surface which isto carry the contact bank is made even and anodised. Then the anodisedsurface is covered by a photosensitive layer of a type that can be usedin making printing plates, and this photosensitive layer is exposedunder a negative which is a representation of the contact elements thatare to be made in the bank. Then the exposed surface is developed in adeveloper suitable for the layer used, as a result of which thephotosensitive layer is removed from the anodised layer on the placeswhere the contact elements are to come. Then the surface is immersed ina fluid that dissolves the anodised layer but does not affect aluminium,and finally the parts of the surface where the original anodised layeris removed are covered by a metal precipitation in a chemical bathsuitable for this purpose, for instance an electroplating bath. Inapplying this method both a photosensitive material which can only bedissolved by the developer after it has been exposed to light as well asa photosensitive material which can be dissolved by the developer buthardens under the influence of light can be used. In the second case thenegative must show the contact elements as dark patches on a diaphanousbackground, whilst in the first case these contact elements must berepresented as diaphanous patches on a dark background. Theprecipitation of the contact metal can be elfected by electrolysis aswell as by reduction.

Experience has shown that in certain circumstances-the method describedabove may lead to imperfections. Nickel, for instance, because of itsexcellent resistance to wear, is a very good material for carrying acontact surface. It is, however, not a simple problem to produce anickel layer which effectively adheres to an aluminium surface. For thispurpose the aluminium surface is generally first covered with zinc, butthe zinc baths used for this purpose are basic and consequently affectthe anodised layer. In connection therewith a further development of theinvention has been undertaken and this has led to an excellentembodiment of a contact bank according to the invention and a specialmethod for making this bank. In this new embodiment the metal contactelements are connected to the aluminium supporting surface by means ofan anodised layer with increased porosity, which covers said surface atthose places where the contact elements are present, the contactelements being connected to the aluminium-surface through the pores inthe layer with increased porosity. In a method for making saidembodiment, between the removal of the anodised layer and theprecipitation of the metal contacts, the parts of the alurninium surfacewhich will have to be covered by the contacts are first covered by ananodised layer with increased porosity in a bath which promotes theporosity of this layer, this layer being made less thick than theanodised layer present beyond the parts where the contacts are to come.

Experience has shown that without any difiiculty an excellently adheringmetal precipitation, such as a nickel precipitation, can be made on thislayer with increased porosity. This precipitation can be effectedelectrolytically as well as by reduction.

The invention will now be described by referring to the particularembodiments shown in the drawing in which:

FIG. 1 shows a partial section of a contact 'elernent'in a contact bankaccording to the invention. FIG. 2 shows a top view of a number ofconcentric contact banks for a digitalising switch which can be madeaccording to the invention.

FIG. 1 shows a partial section of a small part of a contact bankaccording to the invention. The part is situated at either side of theseparation between an isolated part and a contact element, and isgreatly enlarged. The actual thickness of thepart shown is not more than25 The contact bank is carried by an aluminium plate, the upper surfaceof which carries the reference 1. Beyond the contact elements this plateis covered by an anodised layer carrying the reference 2 and consistingof aluminium-oxide. The thickness of this layer is about 20 The contactelement, only a small part of which is shown, consists of two layers,the layer 6 and the layer 3. The layer 3 consists of an electrolyticalprecipitation of semibright nickel. This material is very strong andtough and constitutes an excellent supporting surface for a contactsurface. It is more suitable for this purpose than electrolytical brightnickel, which is so brittle that a contact element consisting of thismaterial will easily come away from its supporting layer as a result oftemperature variations and the differences in expansion resultingtherefrom. The nickel layer does not rest directly on the aluminiumsurface 1. Between this nickel layer and the aluminium surface there isa porous anodised layer 4, which also consists of aluminium oxide buthas a large number of pores such as 5 and has a thickness of 3 to So.This layer causes the nickel layer to adhere better to the aluminiumsurface. The nickel layer is electrically connected to the aluminiumlayer 1 through the pores 5. The surface of the contact element does notconsist of nickel. The passage of current through a contact with anickel surface is not very reliable. The contact resistance of a contactpoint with a nickel surface can sometimes, for no identifiable reason,suddenly increase considerably. In connection therewith the nickel layer3 is made so that its upper surface is slightly lower than that of theanodised layer 2. In a practical embodiment the thickness of the nickellayer is about 12a while the total thickness of the porous anodisedlayer and the nickel layer together is 15;!" This nickel layer iscovered by a thin layer 6 consisting of an electrolytical plating ofhard gold with a thickness of about in. Hard gold is an excellentcontact material. Owing to its hardness it wears only very slightly.Because of the fact that it is carried by a nickel supporting layer nodeformations will occur. In making the contact bank the gold layer ismade slightly too thick. Afterwards the contact bank is polished orlapped, causing the anodised layer and the gold layer to be given acommon plane surface, so that no unevenness will occur at the boundarybetween a contact element and the anodised layer.

In making the contact bank according to the invention the correctdimensions can be maintained within very small limits. The accuracy ofthe dimensions and the situations of the boundaries between contacts andisolating surface are mainly determined by the negative under which thephotosensitive layer is exposed when making the contact bank. Thisnegative can be made in the form of a reproduction in reduced dimensionsof a drawing on a considerably larger scale which may have a highrelative accuracy. This method permits the manufacture of contact banksof very small dimensions and of very great accuracy. This is especiallyimportant in digitalising switches which are to digitalise the positionof a shaft or of an object which can be moved along a straight or anotherwise shaped trajectory.

A reasonably accurate digitalising of such a position will require eightto ten adjacent or concentric contact banks. If these contact banks aremade according to classic methods they become very cumbersome.Digitalising switches with concentric contact banks according to theinvention have, however, been made in which the difference between theradii of two adjacent concentric contact banks is not more than 2 to 2.5millimeters. A combination of ten such concentric contact banks for adigitalising switch that permits an angular position to be digitalisedwith an accuracy which is better than 0.5 degrees, can be built in anembodiment according to the invention on a plate with a diameter with isnot much larger than five to six centimeters. This clearly shows theadvantages of the method according to the invention.

FIG. 2 shows representations of the contact elements of fourconcentrical contact banks of a digitalising switch according to theinvention that can be arranged on one single plate. In manufacturing acontact bank according to the invention one begins with an aluminiumsurface, for instance the surface of an aluminium plate. This surface isground and/ or polished or lapped in order to make it flat and verysmooth. Then this surface is anodised. The anodised layer thus obtainedshould be fairly com- 'pact in order that it may constitute an excellentisolator in the switch and will not be covered by a metal layer when thecontact elements are manufactured by plating. Moreover, this anodisedlayer should be fairly thick; its thickness should be equal to the totalthickness of all the layers which will be incorporated in each spacereserved for a contact element. In a practical embodiment it appears tobe desirable to apply an anodised layer of at least 20 thickness. Such alayer can only be manufactured if it has a small amount of porosity. Itcan be made in a bath containing a few percentages of oxalic acid towhich a voltage of about 70 v. is applied. After this layer has beenmanufactured it is cleaned and then covered with a photosensitive layerof a type which are used in making printing plates. After thisphotosensitive layer has been applied to the anodised layer it isexposed under a negative that is a representation of the contactelements to be made, after which it is developed, so that on the placeswhere the contact elements will be located the photosensitive layer isremoved. Two types of material are available for such photosensitivelayers. One type is naturally soluble in the developer but becomesinsoluble under the influence of light. If such a photosensitive layeris used the negative must show the contacts as dark patches on adiaphanous background. The other type of photosensitive layer isnaturally insoluble and becomes soluble under the influence of light. Ifthis type of layer is used the contacts must be shown on the negative asdiaphanous patches on a dark background, The advantage of this materialfor the photosensitive layer is that it can be successively exposedunder various negatives, causing the sum of the parts shown on thenegatives to become soluble. The result of the development is ananodised aluminium surface which is covered with a protective layerexcept on those parts where the contact elements are to be located. Thissurface is treated with a solution which removes the anodised layer butleaves the aluminium in its original state. An excellent solution forthis purpose is a solution of sodium-dichromate and phosphoric acid inwater at a temperature of about degrees Celsius. This solution removesthe anodised layer completely in those places where it is no longercovered by the photosensitive layer. As soon as the anodised layer hasbeen removed from, and the aluminium surface is uncovered on theseplaces, the plate is cleaned anew and is again anodised in a bath whichaffects the anodised layer while it is being produced. The effect on thenewly anodised layer is the creation of pores. A suitable bath for thispurpose is a 30 percent solution of phosphoric acid at a temperature ofabout 40 degrees Celsius. Actually this bath also affects the originalanodised layer but because the porous anodised layer need only be a verythin one and the making of this porous layer consequently takes only ashort time, the original anodised layer is only very slightly affected.The duration of this second anodising operation is such that a layer ofthe required thickness is manufactured. Generally the application of aphosphoric acid solution as electrolyte does not guarantee a sufiicientporosity. For this reason it is desirable to leave the plate in the bathfor a certain length of time after the current has been switched off.This substantially increases porosity. After the porous layer has beenapplied and the plate has been cleaned again, the metal for the contactelements is precipitated, This can be effected by electrolysis as wellas by reduction. No metal will be precipitated during this operation onthe original anodised layer because this layer is not, or at any rateonly very slightly, porous. Plating will actually occur however, on theporous anodised layers which cover the bottom of each of the openings inwhich contact elements must come. In this operation the pores are firstclosed, and then the plating spreads over the complete surface of theporous layer. Excellent results have been obtained with a plating ofsemi-bright nickel which has good qualities for this purpose. In thefirst place it has a good filling power for macroscopic unevennesses,thus promoting the flatness of the surfaces. Moreover it is a very toughmaterial, providing practically undeformable contact elements.Nevertheless it is not as hard as bright nickel, which, because of itsbrittleness, has the disadvantage that it cannot sufficiently bridge thedifference between its own expansion coeflicient and that ofthealuminium supporting layer, so that greater temperature changes willcause the nickel to separate from the supporting layer.

Electrical Contact established with a nickel surface is not veryreliable. Without any apparent reason the contact resistance of such anickel contact may suddenly be increased. In connection therewith thenickel plating is so made that its upper surface is slightly below thatof the anodised layer, and afterwards a layer of hard gold isprecipitated, for instance electrolytically, on the nickel supportingsurface. Hard gold is an excellent contact material and it is veryresistant to wear so that a contact bank with hard gold contacts remainsreliable for long periods of use. Preferably the layer of hard gold ismade sufficiently thick that it slightly protrudes beyond the originalanodised surface. After the precipitation of the gold the two surfacesare equalised by polishing or lapping, so that even the slightestunevenness near the boundary between a contact and the anodised layer iseliminated.

It is obvious that the various compositions of the baths are onlymentioned as examples and that also other baths which have more or lessthe same effect can be applied. The same is valid for the dimensions andfor the materials for the contact elements. It is, moreover, notabsolutely necessary to connect the contact elements by means of aporous anodised layer to the supporting layer. Without such a porousanodised layer reasonable results may be obtained, but experience hasshown that contact banks provided with such porous anodised layers aremore reliable. The way in which the original aluminium surface has beenplaned is obviously of no importance. Moreover the aluminium surfaceneed not be a part of an independent aluminium plate. As a matter offact aluminium is not a very good construction material, It can beeasily bent, and as soon as the surface layer has been removed, forinstance in an effort to plane the plate, it will in some cases becomewarped. In a very effective embodiment the aluminium surface is onlypart of an aluminium layer, such as an aluminium foil which is fixedlyconnected, for instance by bonding, to a plate of a strongerconstruction material, such as steel.

It would be possible to manufacture the contact elements completely fromhard gold. Hard gold, however, is considerably more expensive thannickel, and although the quantity of the material used in one singlecontact bank is small, the economisation that can be reached bymanufacturing only a part of each contact from hard gold may beconsiderable in the case of mass production of these contact banks.

In many applications the aluminium surface will be fiat but in someapplications it may be necessary to provide a curved surface forsupporting the contact elements. In the former applications withoutspecial measures a flat negative can be used to form the pattern ofcontact element areas in the photosensitive layer.

What I claim is:

1. A switch contact bank comprising an aluminum surfaced support memberhaving a plurality of electrically conductive contact elements thereonand an anodized layer on said support surface between adjacentindividual contact elements, wherein said contact elements comprise alayer of nickel in deposited relation to said support member and a layerof gold in overlying deposited relation to said nickel layer.

2. A switch contact bank according to claim 1 wherein said contactelement further comprises a porous anodized layer between said aluminumsurface and said layer of nickel for mechanically and electricallyconnecting said layers.

3. A switch contact bank according to claim 2 in which said elements arearranged in concentric circular paths.

4. A switch contact bank according to claim 1 wherein the nickel layerof said contact element is semi-bright nickel.

5. A switch contact bank according to claim 2 wherein the surface ofsaid contact elements and the surface of said anodized layer is fiush.

References Cited UNITED STATES PATENTS 3,169,892 2/1965 Lemelson29-155'.5 3,225,269 12/1965 Worcester 336-206 ROBERT K. SCHAEFER,Primary Examiner.

H. O. JONES, Assistant Examiner.

1. A SWITCH CONTACT BANK COMPRISING AN ALUMINUM SURFACED SUPPORT MEMBERHAVING A PLURALITY OF ELECTRICALLY CONDUCTIVE CONTACT ELEMENTS THEREONAND AN ANODIZED LAYER ON SAID SUPPORT SURFACE BETWEEN ADJACENTINDIVIDUAL CONTACT ELEMENTS, WHEREIN SAID CONTACT ELEMENTS COMPRISE ALAYER OF NICKEL IN DEPOSITED RELATION TO SAID SUPPORT MEMBER AND A LAYEROF GOLD IN OVERLYING DEPOSITED RELATION TO SAID NICKEL LAYER.